A load control device for controlling the amount of power delivered to an electrical load (e.g., an LED light source) includes first and second semiconductor switches, a transformer, a capacitor, a controller, and a current sense circuit operable to receive a sense voltage representative of a primary current conducting through to a primary winding of the transformer. The primary winding is coupled in series with a semiconductor switch, while a secondary winding is adapted to be operatively coupled to the load. The capacitor is electrically coupled between the junction of the first and second semiconductor switches and the primary winding. The current sense circuit receives a sense voltage and averages the sense voltage when the first semiconductor switch is conductive, so as to generate a load current control signal that is representative of a real component of a load current conducted through the load.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A load control device for controlling an amount of power delivered to an electrical load, the load control device comprising: a transformer comprising a primary winding configured to conduct a primary current and a secondary winding adapted to supply current to the electrical load; at least one semiconductor switch electrically coupled to generate a primary voltage across the primary winding of the transformer to cause the transformer to transfer power to the secondary winding when the at least one semiconductor switch is conductive; a current sense circuit configured to receive a sense voltage representative of a magnitude of the primary current conducted through the primary winding of the transformer, the current sense circuit comprising an averaging circuit configured to generate a load current signal that is representative of a real component of the primary current by averaging the sense voltage via the averaging circuit when the at least one semiconductor switch is conductive; and a controller configured to generate at least one drive signal for periodically rendering the at least one semiconductor switch conductive for an on time to control a load current conducted through the electrical load in response to the load current signal, the controller further configured to control the current sense circuit to provide the sense voltage to the averaging circuit for the on time plus an additional amount of time to generate the load current signal when a target amount of power to be delivered to the electrical load is less than a threshold amount.
2. The load control device of claim 1 , wherein the additional amount of time is a function of the target amount of power.
3. The load control device of claim 1 , wherein the additional amount of time increases linearly as the target amount of power decreases.
4. The load control device of claim 1 , wherein the controller is configured to control the current sense circuit to provide the sense voltage to the averaging circuit for the on time when the target amount of power to be delivered to the electrical load is greater than the threshold amount.
5. The load control device of claim 1 , wherein the controller is configured to generate a control signal for causing the current sense circuit to provide the sense voltage to the averaging circuit.
6. The load control device of claim 5 , wherein the controller is configured to sample the load current signal when the current sense circuit is being controlled to provide the sense voltage to the averaging circuit.
7. The load control device of claim 1 , wherein the current sense circuit comprises a sense-circuit semiconductor switch configured to disconnect the sense voltage from the averaging circuit, the controller configured to control the sense-circuit semiconductor switch to provide the sense voltage to the averaging circuit when the at least one semiconductor switch is conductive.
8. The load control device of claim 7 , wherein the sense voltage is coupled to the averaging circuit through two series-connected resistors, the sense-circuit semiconductor switch coupled between the junction of the two resistors and a circuit common to allow the sense voltage to be provided to the averaging circuit when the sense-circuit semiconductor switch is non-conductive.
9. The load control device of claim 1 , wherein the at least one semiconductor switch comprises first and second semiconductor switches electrically coupled in series, the controller configured to control the first and second semiconductor switches to generate the primary voltage across the primary winding of the transformer, the transformer configured to transfer power to the secondary winding when either of the first and second semiconductor switches is conductive.
10. The load control device of claim 9 , further comprising: a capacitor electrically coupled between the junction of the first and second semiconductor switches and the primary winding of the transformer to cause the primary voltage across the primary winding to have a positive polarity when the first semiconductor switch is conductive and a negative polarity when the second semiconductor switch is conductive.
11. The load control device of claim 1 , further comprising: a sense resistor coupled in series with the primary winding of the transformer, the sense resistor configured to conduct the primary current and produce the sense voltage.
12. A light-emitting diode (LED) driver for controlling an intensity of an LED light source, the LED driver comprising: a transformer comprising a primary winding configured to conduct a primary current and a secondary winding adapted to supply current to the LED light source; at least one semiconductor switch electrically coupled to generate a primary voltage across the primary winding of the transformer to cause the transformer to transfer power to the secondary winding when the at least one semiconductor switch is conductive; a current sense circuit configured to receive a sense voltage representative of a magnitude of the primary current conducted through the primary winding of the transformer, the current sense circuit configured to generate a load current signal that is representative of a real component of the primary current by averaging the sense voltage when the at least one semiconductor switch is conductive; and a controller configured to periodically render the at least one semiconductor switch conductive for an on time to control a load current conducted through the LED light source in response to the load current signal, the controller further configured to control the current sense circuit to average the sense voltage for the on time plus an additional amount of time to generate the load current signal when a target amount of power to be delivered to the LED light source is less than a threshold amount.
13. The LED driver of claim 12 , wherein the at least one semiconductor switch comprises first and second semiconductor switches electrically coupled in series, the controller configured to control the first and second semiconductor switches to generate the primary voltage across the primary winding of the transformer, the transformer configured to transfer power to the secondary winding when either of the first and second semiconductor switches is conductive.
14. The LED driver of claim 13 , further comprising: an isolated forward converter comprising the transformer and the first and second semiconductor switches, the isolated forward converter configured to receive a bus voltage and to conduct the load current through the LED light source.
15. The LED driver of claim 14 , wherein the isolated forward converter further comprises an energy-storage inductor operatively coupled in series with the secondary winding of the transformer, the energy-storage inductor comprising a partially-gapped magnetic core set.
16. The LED driver of claim 13 , further comprising: a capacitor electrically coupled between the junction of the first and second semiconductor switches and the primary winding of the transformer to cause a primary voltage across the primary winding to have a positive polarity when the first semiconductor switch is conductive and a negative polarity when the second semiconductor switch is conductive.
17. The LED driver of claim 12 , wherein the additional amount of time is a function of the target amount of power.
18. The LED driver of claim 12 , wherein the additional amount of time increases linearly as the target amount of power decreases.
19. The LED driver of claim 12 , wherein the controller is configured to average the sense voltage for the on time when the target amount of power to be delivered to the LED light source is greater than the threshold amount.
20. The LED driver of claim 12 , wherein the current sense circuit comprises an averaging circuit configured to generate the load current signal when the at least one semiconductor switch is conductive, the current sense circuit further comprising a sense-circuit semiconductor switch configured to disconnect the sense voltage from the averaging circuit, the controller configured to control the sense-circuit semiconductor switch to provide the sense voltage to the averaging circuit when the at least one semiconductor switch is conductive.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
January 29, 2019
May 5, 2020
Browse 5M+ US patents with plain-English claim translations and AI-generated analysis.